In order to gain credence as an expert in an academic field of study, you must usually earn a doctorate. Requirements for a doctorate vary by subject and by institution, but the average requirements consist of 48 graduate hours on top of a master's degree, approval of a dissertation (a complex research project examining a previously untested area of study in the candidate's subject area), a comprehensive written exam, and an oral examination.
Experts in the field of medicine have earned a Doctor of Medicine (M.D.) degree from a medical school. Not all medical schools have precisely the same requirements, but elite schools like Stanford University have very high standards for their graduates. Academic or scholarly coursework is necessary, as well as clinical practice in internships, a Clinical Performance Examination and passing scores on the United States Medical Licensing Examination.
Lawyers are considered experts in the general field of law once they have received a law degree and passed their state bar examination. Lawyers can go on to gain expertise in particular specializations by gaining state board certifications in those areas. Law degrees, called Juris Doctor (J.D.) diplomas, typically require 80 to 90 credit hours, from courses, seminars and clinics.
Board certification requirements vary by state and specialization, but they generally mandate a minimum amount of time practicing law in general, and a minimum of time practicing in that specialization, attendance at continuing education classes, positive evaluation by peers, and a written examination.
Expert marksmen have achieved the highest rating within their testing field. While specific requirements vary depending on weapon and organization, the levels usually range from "Marksman" to "Sharpshooter" and then on up to "Expert Marksman." The U.S. Army requires shooters to attain expert status before allowing them to enter training as a sniper.